This invention relates to the measurement of fluid absorbance or turbidity in a pipe line carrying a liquid, fluid, or a gas, and, more particularly, to an optical probe capable of use for both absorbance and high and low-range turbidity measurements, and operable in a number of light energy bands (i.e., wavelengths).
The use of optical systems to measure the characteristics of a liquid or gaseous medium flowing in a pipe, or pipeline transmission system, are well-known in the art. See, for example, my U.S. Pat. No. 4,637,730, which is assigned to the same assignee as the present application. It will be appreciated that such systems are adaptable to both laboratory and industrial applications. Further, such systems are usable with fluid mediums which are corrosive, or in which fluid transmission occurs under extreme temperature and/or pressure conditions. A major benefit of such systems is they permit non-invasive testing of the flowing medium. This eliminates the need to draw off samples into some type of extractive holder, and avoids exposure of personnel to the potential harmful effects of the liquid or gas. It also reduces the potential of an explosion due to an inadvertent spark, etc. As disclosed in the U.S. Pat. No. 4,637,730, a light beam is transmitted through opposed transparent windows. The intensity of the received light is compared with that of a reference beam and the amount of attenuation can be used as a measure of, for example, the turbidity of the fluid. U.S. Pat. No. 4,786,171, also discloses a spectral analysis apparatus and method, wherein it includes the transmission of a light path through a sample being measured, with the light path being adjusted to optimize the amount of light absorbed by the sample, and with the absorbance of the sample being calculated from that length in order to provide measurement of the absorbance of the fluid between two different path lengths, within the measuring device.
While the non-invasive system disclosed in our earlier patent does have certain desirable advantages, it is sometimes also advantageous to be able to insert an optical probe into a sample of gas or liquid. In a production process, for example, such a capability eliminates the need to draw a sample off into an extractive sample holder. As before, this eliminates the chance of employees being exposed to the potentially harmful effects of chemicals, as well as the possibility of an explosion.